Calculating power without distance?

  • Thread starter Thread starter fattydq
  • Start date Start date
  • Tags Tags
    Power
Click For Summary

Homework Help Overview

The discussion revolves around calculating the average power developed by a vehicle that accelerates to a certain speed over a specified time without a given distance. The problem involves concepts from kinetic energy and power in the context of physics.

Discussion Character

  • Conceptual clarification, Assumption checking, Exploratory

Approaches and Questions Raised

  • Participants explore the relationship between kinetic energy and power, questioning the necessity of distance in power calculations. Some suggest that average power can be inferred from energy changes over time, while others express confusion about the role of distance in the formulas.

Discussion Status

The discussion is active, with participants sharing different perspectives on the formulas for power and work. Some guidance is offered regarding the calculation of average velocity and its implications for determining distance, but no consensus has been reached on the best approach to the problem.

Contextual Notes

Participants note the absence of distance in the problem setup, which is leading to uncertainty about how to proceed with the calculations. There is also mention of the constraints imposed by homework rules regarding the use of formulas.

fattydq
Messages
79
Reaction score
0
So here's my homework problem:

Calculate KE of a 1500 kg vehicle moving at 30 m/2. Which I did, and got 675000 joules, using the standard KE formula.

But then it asks, if the vehicle accelerated to this speed in 20 seconds, what average power was developed?

Any formula for power involves a distance, which is not given here at all. Can someone help me out? Is it a trick question?
 
Physics news on Phys.org
fattydq said:
So here's my homework problem:

Calculate KE of a 1500 kg vehicle moving at 30 m/2. Which I did, and got 675000 joules, using the standard KE formula.

But then it asks, if the vehicle accelerated to this speed in 20 seconds, what average power was developed?

Any formula for power involves a distance, which is not given here at all. Can someone help me out? Is it a trick question?

If it acquires its energy in some amount of time, that implies an average power level input during that time interval...
 
As long as the acceleration is constant, the average velocity is the average of the starting and ending velocities. You can use that to find the average kinetic energy.

And I am surprised to hear that "Any formula for power involves a distance". I was under the impression that "power" was "rate of change of energy over time".

(You could, of course, calculate the distance moved at a constant acceleration in a given time. For constant acceleration, a, and time, t, the velocity is at. You can use that to find a from the information given. The distance moved is [itex](1/2)at^2[/itex].)
 
Well the reason I thought I needed a distance was because the formula for power is the change in work over the change in time. SOOOO the formula for work is force times DISTANCE. So I don't understand how can I calculate power if I can't find work.
 
fattydq said:
Well the reason I thought I needed a distance was because the formula for power is the change in work over the change in time. SOOOO the formula for work is force times DISTANCE. So I don't understand how can I calculate power if I can't find work.

It's not change in work, it's amount of work (or energy) in some amount of time.
 
berkeman said:
It's not change in work, it's amount of work (or energy) in some amount of time.

So I just divide the numerical answer for kinetic energy by 20?
 
fattydq said:
So I just divide the numerical answer for kinetic energy by 20?

I believe that is correct.
 

Similar threads

Calculate Avg Power Output for 75kg Person Walking 100ft in 3min
  • · Replies 9 ·
Replies
9
Views
2K
Relating acceleration to distance and time
  • · Replies 5 ·
Replies
5
Views
3K
Calculate the Acceleration of this Car
  • · Replies 7 ·
Replies
7
Views
1K
How many crates can you load in a minute with different average power outputs?
  • · Replies 1 ·
Replies
1
Views
2K
Mechanics (Power): Calculate Horizontal Resistive Force
  • · Replies 6 ·
Replies
6
Views
3K
How Long Does It Take a Car to Climb a Hill with Limited Power?
  • · Replies 2 ·
Replies
2
Views
5K
How Do You Calculate Race Car Acceleration and Power Output?
  • · Replies 20 ·
Replies
20
Views
2K
Finding power without given speed or time
  • · Replies 2 ·
Replies
2
Views
6K
Relativistic motion and length contraction
  • · Replies 44 ·
2
Replies
44
Views
2K
Solving Distance Traveled Using Formulas vs. Graphs
  • · Replies 6 ·
Replies
6
Views
2K